1. Field of the Invention
The present invention relates to a zoom lens used for an image pickup apparatus, such as a video camera and a digital still camera.
2. Description of the Related Art
An image pickup apparatus, such as a video camera, a surveillance camera, a digital still camera, a broadcast camera, which uses an image pickup element, such as a CCD sensor and a CMOS sensor, requires a zoom lens having a small configuration, a wide angle of view, a high zoom ratio, and a high optical performance for a high pixel density of the image pickup element. In particular, a zoom lens having a small F-number is demanded for night photography of a dark object, etc.
In order to satisfy these demands, Japanese Patent Laid-Open No. 2009-204699 (“JP”) discloses a two-unit zoom lens that includes, in order from an object side to an image side, a first lens unit having a negative refractive power, and a second lens unit having a positive refractive power. This two-unit zoom lens varies a magnification by moving the second lens unit in an optical axis direction, and corrects an image-plane fluctuation associated with magnification variations by moving the first lens unit. In addition, this two-unit zoom lens is a vari-focal type zoom lens having a super-wide angle of view exceeding 100°.
JPs 2001-208969 and 2005-099091 disclose a three-unit zoom lens in which a third lens unit is added to the above two-unit zoom lens.
However, the negative/positive type of two-unit zoom lens disclosed in JP 2009-204699 has a difficulty in sufficiently reducing a variety of aberrations, such as a lateral chromatic aberration for the image pickup element having the high pixel density. In addition, the three-unit zoom lens disclosed in JP 2001-208969 has a difficulty in miniaturization due to the increased number of lenses because the third lens unit is added as a fixed unit to the negative/positive type of two-unit zoom lens.
Moreover, the three-unit zoom lens disclosed in JP 2005-099091 is a negative/positive/positive type, and all lens units are configured to be movable. However, its diagonal angle of view is about 80° at the wide angle end or an insufficient wide angle of view. In addition, its F-number is about 2.8 or large (dark).